1. Field
The present teachings relate to a method of recording holographic information, whereby stability of a reproduction signal is secured.
2. Description of the Related Art
Recently, holographic information storing technology has attracted much attention. A holographic data storage unit stores information in a photosensitive material, such as a photopolymer, in the form of an optical interference pattern. The optical interference pattern is formed by using two coherent laser beams, that is, a reference beam and a signal beam, which have different paths and interfere with each other. The optical interference pattern generates chemical or physical change in a photosensitive information storage medium, and thus, is recorded in the photosensitive information storage medium. In order to reproduce information from the interference pattern, the reference beam is radiated on the interference pattern recorded in the photosensitive information storage medium. Accordingly, a diffraction pattern is generated due to the interference pattern, thereby restoring the signal light, and thus, the information is reproduced.
Such information storage technology may be categorized into a volume holography method, whereby recording/reproducing is performed page by page, and a micro holography method, whereby recording/reproducing is performed bit by bit, using individual interference fringes. According to the volume holography method, a massive amount of information is simultaneously processed, but since a very precisely adjusted optical system is generally needed, it is difficult to commercialize volume holography for general consumers.
Meanwhile, according to the micro holography method, information is recorded 3-dimensionally in the information storage medium, by forming minute interference fringes, which are formed by the interference of two concentrated beams, at a focal point. A recording layer generally includes a plurality of such minute interference fringes, and is disposed in plane of the information storage medium. Multiple recording layers are formed at different depths, in the information storage medium.
Generally, according to the micro holographic method, the recording capacity is increased, by forming a plurality of the recording layers. However, noise may be generated while reproducing the information, if pattern stability is not secured in an area on which the interference patterns are recorded.